In existing scrubbed and saturated gas systems such as wet gas scrubbers (WGS) used in the petroleum industry and elsewhere, the offgas may contain NO and/or NO2. These scrubbers may be used in connection with combustion units such as Fluid Catalytic Cracking Units (FCCUs) for the refining of crude oil. Chemicals such as sodium chlorite (NaClO2) can be added to the scrubber liquor in order to oxidize NO to higher oxides such as NO2 and N2O5. These higher oxides are more readily water soluble and can be removed from the system as nitrate and discharged in the wastewater stream.
However, some literature has shown that very high levels of nitrate in water could create health concerns. The nitrate outflow onto shallow continental shelves can produce undesirable near shore algae blooms. Nitrate's role as a plant nutrient can likewise cause undesirable plant growth in other water bodies such as ponds and lagoons. In the United States and Europe, legislation now specifies a maximum permissible nitrate and/or total nitrogen level in water for drinking or industrial discharge. Maximum legal nitrate levels in drinking water are currently 10 mg/liter (NO3—N) in the United States. In the United States, Federal and State Agencies regulate nitrate concentrations in wastewater discharges and groundwater in an effort to reduce impact to the nation's water supply.
In general, prior art wastewater treatment processes have not emphasized the removal of nitrates from the effluent. Prior art techniques for removing nitrates from wastewater have either been ineffective or too expensive. In fact, point source treatment for effluent from, for example, WGS purges has heretofore been generally unavailable. As such, WGS purges containing nitrates and which are also high in salinity have been for the most part treated only with conventional treatment processes which do not address high salinity or high levels of nitrates in the effluent. Conventional secondary wastewater treatment plants are generally designed to primarily reduce carbon and ammonia concentrations via biological treatment. Other known solutions also suffer from various drawbacks such as being overly complex and/or expensive and/or being ineffective.